The invention relates to an apparatus for subliming or condensing a water-containing fluid, which apparatus is provided with a tubular holder having a longitudinal direction and at least one tube extending in that longitudinal direction at least within the holder, wherein the holder is provided with at least one inlet and at least one outlet, there being further provided at least one supply and at least one discharge, which are in communication with the interior of the at least one tube, which extends through a wall of the holder and is sealingly secured therein.
Such an apparatus, as is known from DE-A1-34 41 074, can be used in a method for refining oil or fat, wherein during a deodorization phase, fatty acids, aroma and flavor and other volatile substances are removed from the oil or the fat. This is done, for instance, by contacting the product to be treated, the oil or the fat, with steam of a temperature in the order of magnitude of 200xc2x0 C., the so-called strip steam. The strip steam is, for instance, introduced at the lower end into a vat in which the product to be treated is present and dissolves by-products and impurities, such as fatty acids, from that product. Through an appropriate choice of the parameters, a stable, refined, tasteless and odorless oil can be obtained.
The process referred to works best at pressures of 10 mbar or less. To be able to maintain this reduced pressure in the holder, the strip steam with the impurities dissolved therein is discharged from the vat, whereafter the impurities are to be separated. This is done by supplying the discharged fluid to the holder in which tubes are present which are cooled with a refrigerant, for instance liquid ammonia. The fluid supplied sublimes or condenses on the cooled tubes, so that an ice layer is formed on the tubes. This process is sometimes designated by the name of xe2x80x9cdry condensingxe2x80x9d.
The ice layer forming on the tubes must from time to time be removed in order for the formation of the ice layer, and hence the process, not to come to a halt. Moreover, the energy consumption increases according as the ice layer becomes thicker. Frequent defrosting is therefore necessary to keep the efficiency of the process high and energy consumption low. Frequent defrosting, however, necessitates frequent interruption of the process. This means not only that costly production time is lost, but also that frequent heating up and cooling down is required, which means, in addition to a considerable energy consumption, that the plant is frequently exposed to high shrinkage and expansion forces and hence must be of relatively heavy construction, so that the energy consumption for heating up and cooling down increases still further. Also, a heavy and complicated construction provided with compensation means increases the cost price.
Frequent defrosting can be reduced by using a so-called wet condensing process. In such process, as known, for instance, from U.S. Pat. No. 3,589,104, during condensing or subliming of the water-containing fluid, a liquid film of a temperature approximately equal to that of the refrigerant is passed over the tubes. The water-containing fluid then condenses or sublimes on the liquid film, without this involving freezing on, because the condensed or sublimed water-containing fluid is discharged via the liquid film. Thus, defrosting is not necessary, or at least much less frequently so, but this does not mean that the problems inherent to high shrinking and expansion forces in starting up and switching off the apparatus have thus been remedied.
The object of the invention is to improve an apparatus as referred to in the opening paragraph, such that this apparatus at start-up and switch-off is no longer subject to high shrinking and expansion forces, and thus can be made of considerably lighter and cheaper construction and design, and can be operated with a lower energy consumption.
This is achieved according to the invention in that the at least one tube within the holder terminates with a free end, closed with respect to the interior of the holder, such that the at least one tube within the tubular holder, from the wall in which that tube is sealingly secured, can freely expand and shrink. Through these features, a construction typically comprising a bank of tubes can be realized, which, in contrast to, for instance, tubes extending between two tube plates and secured therein on two sides, is virtually insensitive to shrinkage and expansion stresses, thereby enabling a relatively light construction. An apparatus thus designed is suitable to be used both in a wet condensing and in a dry condensing process, with all the associated advantages of savings of energy and costs.
In particular in case of a typically used tube bank within the tubular holder, it may be provided, in accordance with a further embodiment of the invention, that the free end of each tube is guided so as to be slidable in the longitudinal direction of the tubular holder, by guiding means which are spaced from the wall in which the tubes are sealingly secured. Thus, expansion and contraction of each tube occur in a controlled manner, and the desired configuration of the tubes within the holder is always maintained, so that an optimal flow pattern within the holder can always be effected as well.
By securing the at least one tube on one side, a free internal space can be created in the tubular holder beyond the free end of the tube. This internal free space can be situated adjacent the discharge of the at least one tube. It is preferred, however, that the internal free space is created at the supply. In that case, it is possible, in a further advantageous manner, in accordance with a further elaboration of the invention, that the at least one tube extends substantially parallel to the longitudinal direction of the tubular holder through a first end wall thereof and has its free end terminating before a second end wall, located opposite the first end wall, in or adjacent which, viewed in the direction of the at least one tube, beyond the free end thereof, the at least one inlet is arranged. Through these features, the whole heat exchanging surface of the at least one tube can be optimally utilized, so that the output of the apparatus can be improved.
The possibility of feeding the at least one tube at the free end thereof without adversely affecting the free expansion within the holder is preferably realized in that the at least one tube at or adjacent the free end is connected with the supply by means of a relatively easily bendable connecting tube which has such a length that the free end upon displacement can be smoothly followed through bending. A particularly favorable flow pattern within the at least one tube can then be obtained if the connecting tube has a diameter which is smaller than that of the at least one tube and opens into it with an arrangement eccentric relative to the axis of the at least one tube, with a tangential outflow direction. Thus an optimum distribution of the refrigerant over the inner circumference of the at least one tube can be accomplished and a cooling as uniform as possible can thereby be obtained.
If, as has been noted to be typically the case, a number of tubes are accommodated mutually parallel in the holder, it is preferred, according to a further embodiment of the invention, that the free ends of those tubes are each connected through a connecting tube with a dividing element. In order then to keep the number of breaks through the wall of the holder as low as possible, it is further preferred that the dividing element is disposed within the holder, and the supply linking up with the dividing element extends through a holder wall, so that a single wall interruption can suffice for the supply of the refrigerant.
For similar reasons, for the purpose of applying the apparatus in the wet condensing process, it is preferably provided that at or above the free end of the at least one tube a distribution element is arranged, with which a liquid film can be provided on the at least one tube. For intensifying the contact between the liquid film and the water-containing fluid, it may further be provided that a number of tubes are accommodated mutually parallel in the holder, while at least at one level between the free ends of the tubes and the securing point in the holder wall a baffle plate is arranged over a part of the passage of the holder, which baffle plate, adjacent the at least one tube, is provided with a passage which does not disturb the liquid film.
According to a further embodiment of the invention, it is proposed that a number of tubes are accommodated mutually parallel in the holder, which tubes all terminate on one side outside the holder in a collecting element. True, compared with a collecting element arranged within the holder, such a design involves a greater number of wall interruptions, but they can here be used in an advantageous manner for securing the tubes in the holder on one side, for instance by designing the respective holder wall as a tube plate.
For keeping the tubes in position on the other side, without clamping, it is proposed, according to a further embodiment of the invention, that the guide means comprise at least one strip with at least one passage eye, which passage eye is adapted for longitudinally sliding guidance and positioning of the free end of the at least one tube.